Removed in 2016
This functionality is now accessible from the Power BI Desktop.
All the functionality is still available (and supported in Excel 2016) but the ribbon command has been removed.
The command button is still available and can be added manually by customising the ribbon.
The first time you use this add-in you will be prompted to enable the "Data Analysis Add-ins".
Added in 2013
This works in conjunction with a Power Pivot model.
PowerView provides data visualisations for both PowerPivot models and SSAS databases.
This delivers interactive visualisations including animated visuals and maps powered by Bing Maps.
This was originally only provided as a SharePoint feature.
In Excel 2013 there was an additonal group called "Reports" that appeared on the Insert Tab.
Power View - Inserts a Power View worksheet into the active workbook. Allows you to quickly create data visualizations from tables and charts.